Vacuum circuit breaker

ABSTRACT

A vacuum circuit breaker has contacts and a cylindrically shaped electrode system. A switching arc passes from the contacts to the electrode system. The electrode system comprises an inner cylindrical electrode affixed to one of the contacts and an outer cylindrical electrode concentric with the inner electrode and having a double wall. Voltage is applied to the outer sleeve of the outer electrode. An additional electrode at the potential of the inner electrode is axially adjacent and faces the outer electrode forming a substantially annular canal between the additional and outer electrodes which extends radially at least in part.

United States Patent Schonhuber [s41 VACUUM CIRCUIT BREAKER [22] Filed:July 12, 1971 [21] Appl. No.: 161,772

[30] Foreign Application Priority Data 1 Nov. 14, 1972 3,632,928 1/1972Emmerich et al. .....200/144 B FOREIGN PATENTS OR APPLICATIONS 571,9591/1958 Italy ..200/l44 B Primary Examiner-Robert S. Macon Attorney-CurtAvery et a1.

[ 7] ABSTRACT A vacuum circuit breaker has contacts and a cylindricallyshaped electrode system. A switching arc passes y 16, 1970 Germany 20 360999 from the contacts to the electrode system. The electrode systemcomprises an inner cylindrical electrode [52] US. Cl. ..200/l44 B ffi dto one of the contacts and an outer cylindrical [51] Int. Cl. ..H0lh33/66 electrode concentric with the inner electrode and [58] Field ofSearch ..200/144 B ing a double wall voltage is applied to the outer 56R f sleeve of the outer electrode. An additional electrode 1 e erencesat the potential of the inner electrode is axially ad- UNITED STATESPATENTS jace'nt and faces the outer electrode forming a substantiallyannular canal between the additional and 3,185,800 5/1965 Titus ..200/144 B outer electrodes whigh extends radially at least in part 3,541,28411/1970 Wachta .'...200/l44 B 3,546,406 12/ 1970 Frink ..200/ 144 B 13Claims, 5 Drawing Figures /l/l/l/l/l/ld w/l/l/m PATENTEB Nov 14 I972SHEET 1 BF 5 :Fig.1'

P ATENTEI'JNnv 14 m2 SHEET 2 OF 5 Fly. 2

PATENTEBnuv 14 m2 SHEET 3 BF 5 Fig. 3

PATENTEDnuv 14 I972 I sum u or 5 VACUUM CIRCUIT BREAKER DESCRIPTION OFTHE INVENTION The invention relates to a vacuum circuit breaker. Moreparticularly, the invention relates to a vacuum circuit breaker for highvoltages and high power ratings.

In the design of vacuum circuit breakers it has been attempted for along time to influence the power handling capacity of the breakers andtheir operational properties by the selection of the contact materialand the geometric configuration of the contacts. However, it has becomeknown that the contacts may be associated with a separate electrodesystem to which the arc jumps after being ignited between the contactand in which it is finally quenched or extinguished (U.S. Pat. No.3,509,404). This known arrangement comprises two concentricallydisposed, substantially cylindrical electrodes, the outer of whichcarries a contact or the end face of which functions as the contact. Themovable contacts pass through openings of a carrier to which the innercylindrical electrode is affixed. The contact blocks which are otherwisecustomarily used in vacuum circuit breakers cannot be. utilized in thedescribed arrangement.

An object of my invention is to provide an operationally reliable vacuumcircuit breaker for high voltages and power ratings which uses simpledisc contacts. An object of the invention is to provide a vacuum circuitbreaker having an internal structure which contributes to theachievement of lower contact bum-off,.a lower quenching current andparticularly also of a higher power handling capacity as well as ahigher voltage rating over the specified life.

An object of the invention is to provide a vacuum circuit breaker whicheliminates the need for a vapor shield and its drawbacks. I

Another object of the invention is to provide a vacuum circuit breakerwhich is efficient, effective and reliable in operation.

My invention comprises a vacuum circuit breaker with contacts, fromwhich a switching arc passes over to an electrode system. The electrodesystem comprises a cylindrical inner electrode and an outer electrodeconcentric with the inner electrode and is having a double wall. Voltageis applied to the outer sleeve of the outer electrode. A housingsurrounding the contacts and the electrode system comprises aninsulating body and electrically conductive metal parts closing theinsulating body off at its end faces. In accordance with the invention,one of the contacts is affixed to the inner electrode. Axially adjacentthe double wall electrode is an additional outer electrode which is atthe potential of the inner electrode and faces the outerelectrode,forming an at least partially radially extending substantially annularcanal.

Although in the circuit breaker of the invention the arc is initiallymade to move away fast enough from the contacts, the life of which isincreased thereby, it remains captive in a space completely enclosed byelectrode surfaces until it is quenched or extinguished. The largeelectrode running area available to the arc outside the contactsimmediately results in a substantial reduction of the quenching current.Due to the complete enclosure of the arc space by electrode surfaces,however, migration of the charge carriers from the electrodes orrecombination of charge carriers at surfaces not serving as electrodesis especially prevented. This eliminates the need for an additionalincrease and collection of charge carriers via an anode spot. Anodespots havea tendency to dwell for extended periods at certain points andto erode them excessively. Anode spots do not occur in the circuitbreaker of the invention, and the rapid failure of circuit breakerscaused thereby does not occur below a relatively high critical current.

Since the double wall outer electrode is faced by the additionalelectrode, the arcs are prevented from travelling any distancein theelectrode system, but are efi'ectively repelled after entering into theoppositely disposed sections of the outer and additional outerelectrodes. The arcs may therefore be kept at a safe distance from theinsulating body of the vacuum vessel,

whereby the insulating body is prevented from being sprayed with metalvapor. -A separate vapor shield, which is provided in known vacuumcircuit breakers for the condensation of metal vapor, is thereforeunnecessary and the drawbacks connected therewith are eliminated.

A more favorable stress of the insulating body of the vacuum vessel maybe provided by the two outer mutually facing electrodes, and generallysmaller electrode spacings may be provided within the entire vacuumvessel, as is hereinafter described.

To form the aforedescribed substantially annular canal between the twoouter electrodes, the additional outer electrode may have an outersleeve and be continued radially inward, starting from the end facingthe other outer electrode. The radial configuration can be designed indifferent ways as hereinafter explained.

It is advantageous to the functioning of the electrode system if thecurrent is supplied to the two outer electrodes at the ends of theirouter sleeves. This, together with a practical arrangement of the outerelectrodes, may be accomplished by afiixing the outer sleeves of saidelectrodes to the metal parts at the end faces of the housing of thevacuum circuit breaker.

In order to limit the bum-off of the contacts, it is desirable that thearc from the contacts to the electrode system as rapidly as possible.The speed of this operation may be increased by special design of theouter electrodes. To accomplish this, and in accordance with theinvention, the inner sleeve and the outer sleeve of the first outerelectrode may be separated by an insulating annular gap, and voltage mayalso be applied to the inner sleeve via the corresponding metal part atthe end face. This leads to the formation of a loop in the current path,which propels the arc. The same effect is obtained if the innerelectrode is designed as a hollow cylinder which surrounds the terminalstud and is connected with said stud only at the end provided with thecontact. This design of the inner electrode may be provided in all theembodiments of the invention.

As mentioned, the invention permits the insuring of a favorabledielectric stress of the insulating body of the vacuum circuit breaker.This may be achieved by aligning the outer sleeve of the additionalouter electrode with the outer sleeve of the first outer electrode andarranging the aligned sleeves with a gap parallel to the insulatingbody, the canal formed between the outer electrodes opening at about thecenter of the insulating body. Due to this arrangement, theelectrostatic field builds up relatively uniformly over the middle partof the insulating body and his possible to stay within the stress limitsof the insulating surfaces by a suitable selection of the radii ofcurvature. of the electrodes, while keeping the spacings within thevacuum vessel along the lines of the fringe field small. Information onthe physical basis'for the arrangement of such high voltage electrodesmay be found in Breakdown of Gases Below the Paschen Minimum, IEEE Paper68 TP 647-PWR, 1968.

The desired direction of the switching arcs in the electrode systemdepends on the configuration of the current path. In the region of theadditional outer electrode, the desired return of the arc may beimproved by an insulating gap between the additional electrode and theinner electrode. Different design forms are hereinafter described forthe location of the insulating gap. It is furthermore advantageous forthe design of the vacuum circuit breaker if the additional electrode hasa part approximately aligned with the inner electrode, and theinsulating gap between the aligned parts is in the region of the end ofthe first outer electrode. The desired effect is achieved in the mostreliable manner if, in conjunction with this position of the insulatinggap a double wall first outer electrode is selected with the inner andouter sleeve separated from each other in the indicated manner.

The danger of spraying the insulating body with metal vapor is reducedby the prevention of the are from travelling unchecked in the electrodesystem even before it is within visual range of the insulating body.Additionally, however, such a configuration of the two outer electrodesmay be selected so that they embrace each other in labyrinth fashion.If, furthermore, in another embodiment of the invention, no visualconnection exists between the ends of the substantially annular canalwhich is then labyrinth-shaped, the metal vapor always present in thearc precipitates on the adjacent electrodes and may therefore no longerreach the insulating body. I

In order to' insure that arcs cannot be generated by so-called bypassdischarges, it is recommended that the spacingsbetween electrodes beselected at different potentials about equal to, or partially smallerthan, the spacing of the contacts in the open condition.

For proper operation of vacuum circuit breakers, a high vacuum mustalways be present. Within the scope of the invention, the vacuum mayalso be maintained by having at least one electrode, at least in part,comprise a getter material, without necessarily exerting an unfavorableeffect on the material of the contact proper. By the partial sputteringof the getter material during switching operations immediately prior tothe quenching or extinction of the arc, gases which are possibly presentare then absorbed.

In order that the invention may be readily carried into effect, it willnow be described with reference to the accompanying drawings, wherein:

FIG. 1 is a schematic diagram, partly in section of an embodiment of thevacuum circuit breaker of the invention in which the inner cylindricalelectrode is affixed to the movable contact;

FIG. 2 is a schematic diagram, partly in section of another embodimentof the vacuum circuit breaker of the invention in which the innercylindrical electrode is fixed in position;

FIG. 3 is a schematic diagram, partly in section, of a modification ofthe embodiment of FIG. 2 in which there is a gap between the inner andouter sleeves of the first inner electrode;

FIG. 4 is a schematic diagram, partly in section, of two otherembodiments of the vacuum circuit breaker of the invention, oneembodiment being shown to the right of the center line and the otherembodiment being shown to the left of the center line; and

FIG. 5 is a schematic diagram, partly in section, of still anotherembodiment of the vacuum circuit breaker of the invention having anadditional outer electrode of especially simple structure.

In the FIGS., the same components are identified by the same referencenumerals.

In the embodiment of FIG. 1, the vacuum circuit breaker has a housing 2comprising a pair of discshaped metal parts 3 and 4, arranged at the endfaces, and an insulating body 5 in the form of a hollow cylinder,positioned between the metal parts 3 and 4 and afiixed to said metalparts. The insulating body 5 may comprise glass or ceramic material andmay be smooth or provided with ribs.

In the housing 2, a fixed contact 6 and a movable contact 7 face eachother. Each contact 6 and 7 is of disc, plate or block configuration.The fixed contact 6 may be affixed to the metal part 4, for example,through which the current is supplied. 'A connecting stud 10 is affixedto the metal part 4 and functions as a connection to a bus bar, cable,or the like.

The movable contact 7 is affixed to the end face of an extended,hollow-cylindrical inner electrode 11 which is supported by an actuatorrod 12. The actuator rod 12 also functions as the terminal stud-when itis in the closed condition and immediately after. The inner electrode 11is connected to the actuator rod 12 only at the end at which the contact7 is mounted. The actuator rod 12 extends from the housing 2 through anopening 13 formed through metal part 3 and is movably supported in saidmetal part in a manner not shown in the FIGS. The actuator rod 12 isconnected to a suitable driving mechanism (not shown in the FIGS).Bellows 14 is provided between the metal part 3 and the actuator rod 12to seal the housing 2 with respect to the surrounding atmosphere and topermit vacuum-tight motion of said actuator rod. To relieve the bellows14 from carrying current a connecting strap 15 provides a directelectrically conductive metal connection between the actuator rod 12 andthe metal part 3.

A first outer electrode 16 and an additional outer electrode 17 arepositioned in the housing 2 axially adjacent each other and concentricto the inner electrode 11. The first outer electrode 16 and theadditional outer electrode 17 direct the arc ignited between thecontacts 6 and 7 in a manner hereinafter described. The first outerelectrode 16 has a double wall which in its cross-sectionalconfiguration is approximately a U.

The open end of the first outer electrode 16 faces the metal part 4. Thefirst outer electrode 16 has an inner sleeve 20 and an outer sleeve 21which is affixed to the metal part 4 at the end face. The inner sleeve20 is shorter than the outer sleeve 21. A current entering the electrode16 therefore always flows through the sleeve 21 to the metal part 4. Astep 22 is provided between the sleeves 20 and 21 of the first outerelectrode 16 in such a manner that there is a small space 22' betweenthe sleeves 20 and 21 at the upper end of the first outer electrode 16which expands to a larger space 23 between said sleeves.

. The additional outer electrode 17 has essentially the same shape asthe first outer electrode 16. The additional outer'electrode 17- thushas an inner sleeve 24 which surrounds the inner electrode 11concentrically with a substantially annular gap 28, and an outer sleeve25. A step 26 is provided between the sleeves 24 and of the electrode17, similarly to the step 22 of the electrode 16. The outer sleeve 25 ofthe electrode 17 is affixed to the metal part 3 at the end face of thehousing 2, whereby the potential of the inner electrode 11 is applied tothe additional outer electrode 17.

It is essential for the arrangement of the electrodes 16 and 17 thatthey engage in labyrinth fashion in such a manner that a substantiallyannular canal 27 having a substantially Z-shaped cross-section isformed; the canal 27 having two radially extending sections and oneaxially extending section. Since the operating voltage of the vacuumcircuit breaker is applied to the outer electrodes 16 and 17, the stressof the insulating body 5 is shifted to its central zone from the openingof the canal 27. A favorable distribution of the electrostatic field isprovided. By appropriate dimensioning of the radii of curvature 30 and31 at the outer opening of the canal 27, as well as by suitablydimensioned gaps 32 and 33 between the outer sleeves 21 and 25,respectively, and the insulating body 5, electrical overstressing of thesurface of said insulating body is avoided. Increasing the spacing ofthe electrodes along the lines of the electric field going substantiallybeyond the width of the contact opening is therefore unnecessary. Due tothe aforedescribed favorable field distribution, a high dielectricstrength is provided along the insulating body 5, and in conjunctionwith the reliable arc return from the canal 27 a very substantialreduction in the spraying of the inner surface of said insulating body 5is achieved. This results in increased life of the circuit breaker ofthe invention even at the highest power ratings.

Upon switching off, the contacts 6 and 7 arrive at the positions shownin FIG. 1. The are ignited between the contacts 6 and 7 travels into thesubstantially annular gap between the inner electrode 11 and the firstouter electrode 16 through the influence of the magnetic field. The aremay travel in such gap upwards until it is taken over by the additionalouter electrode 17, which is at the same potential as the innerelectrode 11. If the arc is not yet quenched or extinguished by then, itmay enter into the Z-shaped canal 27. There, however, a magneticinfluence on the arc occurs in such a manner that it is repelledefiectively and immediately. The are can therefore not get within viewof the wall of the insulating body 5 and damage it or spray it withmetal vapor. This is aided particularly by the fact that there is novisual connection to the insulating body 5 from the entrance of theZ-shaped canal 27, which is situated between the topmost point 29 of thefirst outer electrode 16 and the step 26 of the additional outerelectrode 17.

The vacuum circuit breaker of the embodiment of FIG. 2 is completelysimilar to the breaker of the em-' bodiment of FIG. 1 with respect toits basic design and operation. However, in the embodiment of FIG. 2there is a change in the arrangement of the contacts 6 and 7 since theinner electrode 11 is provided in fixed relation with the contact 7 andthe contact 6 is movably mounted. Accordingly, the bellows 14 isprovided at the metal part 4 at the end face, and the contact 6 isaffixed to a movably-mounted carrier 36. As in the embodiment of FIG. 1,a connecting strap 15 functions to relieve the bellows 14' from carryingcurrent. The first inner electrode 16 is provided with slots 35.

In the modified vacuum circuit breaker of FIG. 3, in contrast to theother embodiments, the inner sleeve 20 of the first outer electrode 16is also affixed to the metal part 4 at the end face of the vacuum vessel2, and an annular insulating gap 34 is formed in the region of the upperend 29 of said first outer electrode 16. The insulating gap 34 may belocated directly at the topmost point or somewhat below such point onthe side facing the inner electrode 11, or on the side facing away fromit.

- The parts of the electrodes adjacent the annular insulating gap 34 maybe rounded off by a bead, or an overlap can be provided in lieu of therounding off, as indicated in the embodiment of FIG. 4. This structureof the first outer electrode 16 provides the advantage that after thearc leaves the vicinity of the contacts 6 and 7 an intensive loop effectis exerted which moves the are rapidly toward the upper end 29 of saidelectrode. As soon as the arc passes to the additional outer electrode17, however, and enters the canal 27, it is prevented from travellingfurther, by a strong loop effect, and is repelled.

In the embodiments hereinbefore described, a part of the additionalouter electrode 17, which is at the potential of the inner electrode 11,extends parallel to said inner electrode, as the sleeve 24, to maintainthe annular gap 28. FIG. 4 shows two modifications for the design of theouter electrodes 16 and 17 and the inner electrode 11 which permit anadditional influence on the arc.

In the left part of FIG. 4, another additional outer electrode 18 isprovided. The other additional outer electrode 18 has an inner sleeve 24which is modified in such a way that it protrudes radially inwardly as alinear continuation of the step 26 of the electrode 17 (FIG. 1). Theinner electrode 11' is shortened and also drawn inward, so that thesubstantially annular gap 28' remains, but in a different position. Thisresults in a reliable engagement of the are at the entrance of the canal27'.

In the right part of FIG. 4, another additional outer electrode 19 isprovided. The other additional outer electrode 19 has an inner sleeve24", contrary to the embodiments of FIGS. 1 to 3, which is angled offdownward from the metal part 3 on the end face, that is, in thedirection of the metal part 4 on the end face. Furthermore, the innerelectrode 11" is shortened so that the end of the shortened electrode11" and the end of the inner sleeve 24' face each other in a mannersimilar to the inner and outer sleeve of the electrode 16 of FIG. 3. Itis recommended, however, that the gap 28" be provided between the innerelectrode 11" and the outer electrode 19 at a different height than thegap 34 of FIG. 3. The ends of the electrodes 11" and 18 or 19,respectively, facing each other may suitably overlap each other, asshown in FIG. 4.

The changed direction of the inner sleeve 24" of the outer electrode 19in the right hand part of FIG. 4 causes an extension of thelabyrinth-like overlap between the two outer electrodes 16' and 19. Thechance that metal vapor might get on the insulating body 5 is thereforeparticularly small. This is aided by the fact that the differentposition of the gap 28 between the electrodes 11'. and 19 repels the arcafter the arc enters the labyrinth-like overlap of the outer electrodes16' and 19, even earlier than in the aforedescribed embodiments.

It is known to produce in vacuum circuit breakers a rotation of the arecaused by its own magnetism by slots formed in the contacts or theelectrodes associated with them. Such slots may also be usedadvantageously in the electrode system of my invention, extending at anangle to the axis. Under some conditions, a favorable effect may beobtained if only one of the electrodes is slotted simply in the axialdirection; but all three electrodes may be provided with slots. In theembodiment of FIG. 2, the double wall first outer electrode 16 has slots35 formed therein at inclinations to the axis. The slots 35 are formedin the outer sleeve 21 (FIG. 2).

Individual features of the described embodiments may also be combinedwith one another in order to correct the magnetic effect on the arc. Forexample, the design of the electrodes 11', 11", 18 and 19 may beutilized, regardless of whether the first outer electrode 16 is dividedand has a gap 34 at its topmost point (FIG. 4).

FIG. 5 illustrates another embodiment of the invention having aparticularly simple design of the double wall first outer electrode 40and the additional outer electrode 39. The additional outer electrode39, starting at its outer sleeve 25 extends radially inward at a rightangle and then again at a right angle axially toward the metal part 4 onthe end face. The double wall first outer electrode 40 is of simplerstructure than in the aforedescribed embodiments.

The first outer electrode 40 is of U-shaped cross-section, except forthe substantially annular gap 34 in the same position as in theembodiment of FIG. 4. The inner sleeve 41 and the outer sleeve 42 of thefirst outer electrode 40 are hollow cylinders positioned concentricallyaround the actuator rod 12 and connected by a radially extending part43. The inner electrode 11" has the shortened configuration illustratedin the right hand part of FIG. 4 with a constriction at its upper endthereby forming a substantially annular gap 28" with the additionalouter electrode 39.

In FIG. 5, the canal 44 between the electrodes 39 and 40 is of simpleangular configuration. There is no visual connection between theentrance of the canal 44, which is at the mutually staggeredsubstantially annular gaps 28" and 34, and the opening at the insulatingbody 5, as in the aforedescribed embodiments. This is essential for theprotection of the insulating body 5 from spraying with metal vapor.

While the invention has been described by means of specific examples andin specific embodiments, I do not wish to be limited thereto, forobvious modifications will occur to those skilled in the art withoutdeparting from the spirit and scope of the invention.

I claim:

- 1. A vacuum circuit breaker having a housing comprising an insulatingbody of substantially hollow cylindrical configuration and a pair ofelectrically conductive metal parts closing the insulating body at theend faces thereof, first and second contacts and an electrode system inthe housing in which a switching arc passes from the contacts to theelectrode system, the electrode system comprising an inner electrode ofsubstantially hollow cylindrical configuration and a first outerelectrode of substantially hollow cylindrical configuration having adouble wall with an inner sleeve and an outer sleeve concentricallypositioned around the inner electrode, means for applying a voltage tothe outer sleeve of the first outer electrode, the vacuum circuitbreaker comprising an additional outer electrode at the potential of theinner electrode axially adjacent the first outer electrode and formingtherewith a substantially annular canal extending radially at least inpart, one of said contacts being affixed to the inner electrode.

2. A vacuum circuit breaker as claimed in claim 1, wherein theadditional outer electrode has an outer sleeve extending substantiallyparallel to the inner electrode and continuing radially inward from theportion thereof opposite the first outer electrode, and an inner sleeve.

3. A vacuum circuit breaker as claimed in claim 1, wherein theadditional outer electrode has an outer sleeve affixed to one of themetal parts of the housing and extending substantially parallel to theinner electrode and continuing radially inward from the portion thereofopposite the first outer electrode, and an inner sleeve, and the outersleeve of the first outer electrode is affixed to the other of the metalparts of the housing.

4. A vacuum circuit breaker as claimed in claim 1, wherein the firstouter electrode has a substantially annular insulating gap formedtherein separating the inner sleeve and the outer sleeve thereof, andfurther comprising means for applying a voltage to the inner sleeve ofthe first outer electrode via one of the metal parts of the housing.

5. A vacuum circuit breaker as claimed in claim 1, wherein theadditional outer electrode has an inner sleeve and an outer sleevealigned with the outer sleeve of the first outer electrode, the outersleeve of each of the first and additional outer electrodes extendingsubstantially parallel to the insulating body of the housing but spacedtherefrom by a gap, and wherein the canal opens approximately at thecenter of the insulating body of the housing.

6. A vacuum circuit breaker as claimed in claim 1, wherein the electrodesystem further comprises a substantially annular insulating gap betweenthe inner electrode and the additional outer electrode.

7. A vacuum circuit breaker as claimed in claim 1, wherein theadditional outer electrode has a part extending substantially parallelto the inner electrode and forming therewith a substantially annularinsulating gap in the area of the upper end of the first outerelectrode.

8. A vacuum circuit breaker as claimed in claim 1, wherein theadditional outer electrode embraces the first outer electrode inlabyrinth fashion.

9. A vacuum circuit breaker as claimed in claim 1, wherein theadditional outer electrode embraces the first outer electrode inlabyrinth fashion with no visual connection between the ends of thecanal.

10. A vacuum circuit: breaker as claimed in claim 1, wherein the firstand second contacts are spaced a predetermined distance in opencondition and each of the inner and first outer electrodes and the firstand additional outer electrodes are spaced from each other by a distancehaving a maximum magnitude equal to the predetermined distance.

11. A vacuum circuit breaker as claimed in claim 1, wherein at least oneof the inner electrode, first outer electrode and additional outerelectrode at least partially comprises getter material.

12. A vacuum circuit breaker as claimed in claim 1,

1. A vacuum circuit breaker having a housing comprising an insulatingbody of substantially hollow cylindrical configuration and a pair ofelectrically conductive metal parts closing the insulating body at theend faces thereof, first and second contacts and an electrode system inthe housing in which a switching arc passes from the contacts to theelectrode system, the electrode system comprising an inner electrode ofsubstantially hollow cylindrical configuration and a first outerelectrode of substantially hollow cylindrical configuration having adouble wall with an inner sleeve and an outer sleeve concentricallypositioned around the inner electrode, means for applying a voltage tothe outer sleeve of the first outer electrode, the vacuum circuitbreaker comprising an additional outer electrode at the potential of theinner electrode axially adjacent the first outer electrode and formingtherewith a substantially annular canal extending radially at least inpart, one of said contacts being affixed to the inner electrode.
 2. Avacuum circuit breaker as claimed in claim 1, wherein the additionalouter electrode has an outer sleeve extending substantially parallel tothe inner electrode and continuing radially inward from the portionthereof opposite the first outer electrode, and an inner sleeve.
 3. Avacuum circuit breaker as claimed in claim 1, wherein the additionalouter electrode has an outer sleeve affixed to one of the metal parts ofthe housing and extending substantially parallel to the inner electrodeand continuing radially inward from the portion thereof opposite thefirst outer electrode, and an inner sleeve, and the outer sleeve of thefirst outer electrode is affixed to the other of the metal parts of thehousing.
 4. A vacuum circuit breaker as claimed in claim 1, wherein thefirst outer electrode has a substantially annular insulating gap formedtherein separating the inner sleeve and the outer sleeve thereof, andfurther comprising means for applying a voltage to the inner sleeve ofthe first outer electrode via one of the metal parts of the housing. 5.A vacuum circuit breaker as claimed in claim 1, wherein the additionalouter electrode has an inner sleeve and an outer sleeve aligned with theouter sleeve of the first outer electrode, the outer sleeve of each ofthe first and additional outer electrodes extending substantiallyparallel to the insulating body of the housing but spaced therefrom by agap, and wherein the canal opens approximately at the center of theinsulating body of the housing.
 6. A vacuum circuit breaker as claimedin claim 1, wherein the electrode system further comprises asubstantially annular insulating gap between the inner electrode and theadditional outer electrode.
 7. A vacuum circuit breaker as claimed inclaim 1, wherein the additional outer electrode has a part extendingsubstantially parallel to the inner electrode and forming therewith asubsTantially annular insulating gap in the area of the upper end of thefirst outer electrode.
 8. A vacuum circuit breaker as claimed in claim1, wherein the additional outer electrode embraces the first outerelectrode in labyrinth fashion.
 9. A vacuum circuit breaker as claimedin claim 1, wherein the additional outer electrode embraces the firstouter electrode in labyrinth fashion with no visual connection betweenthe ends of the canal.
 10. A vacuum circuit breaker as claimed in claim1, wherein the first and second contacts are spaced a predetermineddistance in open condition and each of the inner and first outerelectrodes and the first and additional outer electrodes are spaced fromeach other by a distance having a maximum magnitude equal to thepredetermined distance.
 11. A vacuum circuit breaker as claimed in claim1, wherein at least one of the inner electrode, first outer electrodeand additional outer electrode at least partially comprises gettermaterial.
 12. A vacuum circuit breaker as claimed in claim 1, wherein atleast one of the electrodes has slots formed therein.
 13. A vacuumcircuit breaker as claimed in claim 1, further comprising a terminalstud extending into the housing through one of the metal parts thereofand having one of the first and second contacts mounted at one end ofthe stud in the housing, and wherein the inner electrode isconcentrically positioned around the stud and is affixed to the studonly at the end mounting the one of the contacts.